1. Field of the Invention
The invention relates to mass spectrometry, mass spectrometers and applications thereof.
2. Description of the Related Art
Mass spectrometers provide a fundamental tool of experimental chemistry and have proven useful and reliable in identification of chemical and biological samples. Mass spectrometry is a technique used to determine the masses of molecules and specific fragmentation products formed following vaporization and ionization. Detailed analysis of the mass distribution of the molecule and its fragments leads to molecular identification. The combination of specific molecular identification and extreme sensitivity makes molecular spectroscopy one of the most powerful analytical tools available.
However, the typical mass spectrometer is confined to the laboratory or other fixed sites due to its relatively large size and weight, as well as its high power and cooling requirements. Thus, mass spectrometer technology has not been used as a field portable detection system. Other impediments to field use include large storage reservoirs of samples that are typically required for reliable identification, whereas field samples are often much smaller and detection of such small samples is often essential (for example, in the case of detection of a chemical or biological agent that is lethal at small doses).
Thus, there is typically an abundant sample available for analysis in mass spectrometers located in a laboratory or in a commercial setting. Thus, a highly resolved spectrum may be achieved by repeated ionization and detection of the analyte. By contrast, in the field, only a small and diffuse sample maybe available for collection from the environment. In addition, samples collected in the field (for example, a soil sample that only contains trace amounts of an explosive) may not be adequate for identification of a chemical or biological agent contained therein even if transported to a laboratory grade mass spectrometer.
A significant related problem arises in chemical vapor detection of certain substances using mass spectroscopy. For example, chemical vapor detection of certain important substances that require detection, such as drugs and explosive compounds, is hindered by their extremely low vapor pressures. For example, the equilibrium vapor pressure of trinitrotoluene (TNT) is 10xe2x88x929 atm and RDX it is 10xe2x88x929 atm. For these types of vapor concentrations, it is difficult for even the highly sensitive detection performed by a mass spectrometer to accurately measure concentrations.
For these compounds, a different detection technique relies on the principle that vapor pressure of a substance increases exponentially with increasing temperature. Hence, for certain applications such as batch sampling of suspected packages, the detection community has implemented a technology based on collection of particulate matter from contaminated surfaces by wiping or vacuuming onto a filter media. The sample is then heated to a point where it develops sufficient vapor pressure to enable vapor phase detection. This approach, however, is extremely slow, inefficient and, considering the bulk thermal treatment of the sample media, very power hungry.
Among other things, it is thus an object of the invention to provide a system and method that provides an efficient collection of particulate samples for analysis by a mass spectrometer. It is a further objective of the invention to provide a system and method that efficiently vaporizes a substance of interest (i.e., a particular chemical or biological agent) that is then provided in a highly concentrated amount to an extraction stage of a mass spectrometer. Finally, it is an objective to implement both of the aforementioned objectives in a field portable mass spectrometer.
In accordance with these objectives, the invention provides a mass spectrometer system comprising a laser and a mass spectrometer. The mass spectrometer has a vacuum interface that provides entrance of a gaseous sample into an extraction region of the mass spectrometer. The laser is positioned to provide laser light incident on a sample nongaseous substance positioned adjacent the vacuum interface. The laser light provides vaporization of the sample, which provides a high concentration of gaseous molecules from the sample substance at the vacuum interface.
The invention also provides a method of analyzing a non-gaseous sample for a compound of interest. The method includes generating laser light having at least one parameter adjusted to provide enhanced vaporization of the compound of interest from the sample. The laser light is directed so that it is incident on the sample for at least one time interval, thereby vaporizing at least part of the sample. A collection of at least a portion of the vapor is synchronized with the at least one time interval. A chemical vapor analysis of the portion of the vapor collected is performed, the chemical vapor analysis including determining whether the substance of interest is present in the sample.